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Faculty for Biology, Chemistry, and Earth Sciences

Soil Physics

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Finished Theses

Bachelor's Theses
Henri Michael Braunmiller (2020) Impact of soil drying on mucilage production and rheology

Mucilage is a polymeric gel containing polysaccharides and lipids. It is exuded by the root tips and holds large amounts of water. This keeps the rhizosphere moist, especially under dry conditions. With higher variability of rainfall and more extreme weather events (e.g. drought) caused by the human made climate change, this could be an important trait for our crops to maintain a constant yield even under unfavorable conditions.

The idea of my project is to show the effect of variety and water availability on the production of mucilage and its rheological parameters. Therefore I use two different maize varieties (B73 and Mo17) and two different water contents. The mucilage is being measured and compared for its amount, viscosity and surface tension value. In addition, we will observe the behavior of the mucilage in soil using a neutron radioscope. This allows us to measure it without intercepting the soil.

Supervisor: Mutez Ali Ahmed, Andrea Carminati

Master's Theses
Anna Sauer (2020) Investigating drought traits in sorghum landraces - A lysimetric experiment in four soil textures

Water availability is a primary limitation to crop production and depends on water input and soil texture, among others. A huge variety of sorghum landraces promises unexplored traits to overcome water stress, like high transpiration efficiency or early maturity.

 To test these, four sorghum landraces and one elite line were grown in four soil textures in a lysimetric facility in ICRISAT, India. Nitrogen fertilization was either added by mineralized or organic sources. The soil was dried down to 30 % usable field capacity. Weekly measured transpiration and data of biomass, plant development, yield and more will be analyzed and may reveal traits to overcome drought stress.

Supervisor: Mutez Ali Ahmed, Andrea Carminati, Jana Kholova
Tina Köhler (2020) Emerging effects of root hairs and soil properties on soil-plant water relations under drought conditions

Limited water supply is one of the largest impediments to food production worldwide. Therefore, improving crop management of soil water depletion will be important to sustain the increasing food demand. The effect of belowground processes on transpiration and stomatal regulation remains controversial. Objective of this study was to understand the role of rhizosphere properties and processes, namely soil textural properties and root hairs, on transpiration, leaf water potential and stomata conductance with soil drying. We hypothesize that 1.) root hairs facilitate the water extraction from drying soils. This is expected to be reflected in the relation between transpiration rate and leaf water potential. Moreover, we expect 2.) different soil textures to affect root water uptake differently and therefore the relationship between leaf water potential and transpiration.

We compared maize (Zea mays L.) with (wild-type) and without (rth3-mutant) root hairs in three different soils (Alfisol, Vertisol and Sandy Soil) with different textural properties (loamy, clayey, sandy), respectively. Transpiration and leaf water potential were monitored, and stomata conductance calculated with decreasing soil water content and potential.

The hairless mutant declined transpiration at greater water contents or/ and exhibited lower transpiration rates in dry soils as compared to the wild-type. The relationship between leaf water potential and transpiration/ stomata conductance did not differ between genotypes, most likely because of prompt stomata closure. Moreover, plant transpiration responses to declining soil water content and – potential differed considerably between soils. Soil hydraulic characteristics and features like soil cracking in Vertisol as well as soil crust formation in Alfisol are believed to have influenced those relations. The relationship between transpiration and leaf water potential varied strongly between soils as well but stomata response to decreasing leaf water potential showed no direct sensitivity to soil texture. Therefore, we conclude that soil texture indirectly affected stomata by changing the soil-plant conductance.

In conclusion, this study provides experimental evidence of the strong link between stomata regulation and soil-root hydraulic properties. Further experiments will be needed for clarification and quantification.

Supervisor: Mutez Ali Ahmed, Andrea Carminati
Asegidew Akale (2020) Phenotypic differences of root exudates and their impact on drought tolerance across different varieties of maize.

Mucilage provides benefits for plant growth by maintaining the rhizosphere's water content during soil drying. The aerial root of maize (Zea mays L.) releases a significant amount mucilage to the rhizosphere. However, scarce information is available on quantitative and qualitative differences between the root exudation profile of the landrace and hybrid maize.

In this study, we find that mucilage production in the landrace is significantly different. The mucilage ability to store water potentially makes the landrace less vulnerable to drought. The variations of mucilage production in Maize cultivar would be significant for further analysis of crop adaptation to environmental stress.

Supervisor: Andrea Carminati, Mutez Ali Ahmed
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